how to define breaks in mkpp()?

mkpp(breaks,coefs);

If I have 256 coefficients then how can I define breaks?

[Avinash Bhatt]

if I have a matrix of 256 coefficients, suppose :

X=imread('cameraman.tif');

and I want to create the piecewise polynomial structure using mkpp(breaks, coeffs) where coeffs will be the pixel intensity values then how breaks can be defined.